A comparative epidemiological and environmental study in two neighbouring villages, Karain and Karlin, in Central Turkey showed an excess adult mortality, shortening of life expectancy, and an excess of pleural radiological abnormalities in Karain. This supports an earlier report of an endemic of pleural mesothelioma in the village. Concentrations of airborne respirable fibres were uniformly very low in Karlik and higher in some of the air samples from Karain, the fibres being similar in composition to those of erionite-a mineral of the zeolite family and the major contributor to the Karain clouds. This is compatible with the hypothesis of a causal association between endemic mesothelioma and inhalation of erionite fibres, but the fibre concentrations in all samples are so low as to leave in question the aetiological role of erionite. In addition to their local importance these results may have relevance for the wider scientific and public-health issue of long-term inhalation of mineral fibres at low concentrations.